1. Field of the Invention
The present invention relates to acoustic equipment.
2. Description of the Related Art
Sound-direction detectors have a wide range of applications, such as (i) in speech recognition systems, to steer microphones to help separate speech from other sound sources; (ii) in robotics, to direct cameras to a sound source; (iii) in safety devices, e.g., to alert a deaf person; and (iv) in military devices, to help detect the source of enemy fire. A typical prior-art sound-direction detector employs a sound-direction sensor having multiple, spatially-distributed microphones that are separated by distances comparable to or larger than the wavelength of sound. Signals received from a sound source by different microphones have small differences due to different sound propagation paths. These differences are measured by the detector and the measurement results are processed to obtain the sound-direction information.
Vowel and consonant sounds in human speech have average wavelengths (frequencies) of about 110 mm (3 kHz) and 66 mm (5 kHz), respectively. As a result, a prior-art speech-direction sensor has a linear size of at least about 10 cm. Sound-direction sensors for other types of sound have similar dimensions. Attempts to miniaturize these prior-art sensors, e.g., to a linear size of several millimeters, while maintaining the angular accuracy of several degrees, have been largely unsuccessful because signal differences for microphones separated by several millimeters tend to be very small. Consequently, the sound-direction information extracted from such small differences disadvantageously lacks the requisite accuracy.